Now this is cool and I can see how this can be very useful in a number of scenarios. In his latest SnTT post Egor Margineanu, Notes/Domino blogger from Moldovia, is using the Java extensionability of the Java XSLT processor he uses (Saxon) to evaluate @formulas in computed text. Very nice! Check it out.
Direct link to post: SnTT: Evaluate @-formula in XSL transformation